Blockwise Self-Attention for Long Document Understanding (1911.02972v2)

Abstract: We present BlockBERT, a lightweight and efficient BERT model for better modeling long-distance dependencies. Our model extends BERT by introducing sparse block structures into the attention matrix to reduce both memory consumption and training/inference time, which also enables attention heads to capture either short- or long-range contextual information. We conduct experiments on LLM pre-training and several benchmark question answering datasets with various paragraph lengths. BlockBERT uses 18.7-36.1% less memory and 12.0-25.1% less time to learn the model. During testing, BlockBERT saves 27.8% inference time, while having comparable and sometimes better prediction accuracy, compared to an advanced BERT-based model, RoBERTa.

• The paper introduces a blockwise sparse attention mechanism that reduces memory use by up to 36.1% while efficiently capturing long-range dependencies.
• The method significantly improves training and inference speeds, cutting training time by 12.0%–25.1% and inference time by about 27.8%.
• Extensive experiments validate that this approach maintains or enhances model accuracy compared to dense attention models like RoBERTa.

Blockwise Self-Attention for Long Document Understanding

The paper "Blockwise Self-Attention for Long Document Understanding" introduces a novel approach to improving the computational efficiency of BERT-based models when processing long sequences. This research addresses a critical limitation in the transformer architecture, particularly the memory-intensive nature of the dot-product self-attention mechanism, which scales quadratically with sequence length. The authors propose a sparse block structure within the attention matrix designed to maintain model performance while dramatically reducing computational resource demands.

Key Contributions and Methodology

1. Sparse Block Matrix Architecture: The authors introduce a blockwise attention mechanism that divides the attention matrix into sparse blocks. This innovation facilitates efficient modeling of long-distance dependencies within sequences, reducing memory consumption and computational load. By creating a sparse block structure, the method leverages the capacity to capture both short-range and long-range dependencies across multiple attention heads without necessitating the memory of a fully dense matrix.
2. Performance Metrics and Improvement: The proposed model, labeled as Bert, demonstrates significant improvements in memory efficiency and training time while maintaining, and in some cases enhancing, model accuracy. Specifically, memory usage is reduced by 18.7% to 36.1%, and training time is curtailed by 12.0% to 25.1% across various tasks compared to RoBERTa, a recent BERT derivative.
3. Experimental Validation: Extensive experimental validation was conducted on multiple datasets and tasks, including LLM pre-training and several benchmark question-answering datasets with varying paragraph lengths. Notably, Bert reduces inference time by approximately 27.8%, showcasing its efficiency for large-scale application deployment.

Implications and Future Directions

The implications of this work are significant for both theoretical advancements in natural language processing and the practical deployment of AI models. The reduction in computational overhead without compromising model performance could facilitate broader adoption of large-scale models in real-time applications, especially where resource constraints are prevalent.

Theoretically, this approach opens up avenues for further optimization of Transformer architectures, encouraging exploration into other forms of structured sparsity and the integration of additional mechanisms for contextual embedding.

Future research may focus on extending this model to more diverse NLP tasks beyond question answering, such as document-level machine translation or protein sequence modeling, where long-context comprehension is essential. Furthermore, benchmarking against other emergent efficient transformers could provide additional insights into optimizing self-attention mechanisms.

Collectively, this paper contributes towards the efficient scaling of BERT-based models and sets a foundation for broader exploration into sparsity-driven optimization in deep learning architectures.